This invention relates generally to switches, and more specifically to a magnetoplasmadynamic switch capable of transferring large magnitudes of power.
The generation of powerful current pulses requires a convenient energy source that must store the necessary energy, and transform and deliver it at very high electromagnetic power rates (i.e., short discharge times).
Various energy sources exist, whose typical discharge times vary from submicrosecond to multisecond. Among the systems used most is the capacitor bank, becuase of its flexibility and high transfer efficiency. Inductive storage is an alternative to the capacitive storage of energy. Here a primary energy source supplies a current to a storage inductance and the stored energy is then transferred with a certain efficiency to a load inductance by increasing the impedance in a common branch until the common circuit branch is interrupted. Efficient circuit interrupters capable of carrying current for moderate periods of time, hundreds of microseconds long, and then opening in a short period of time, of a few microseconds or less, at high voltages to transfer megajoules are not believed to exist.
The reason may be understood from the following analysis. In order to transfer current to an inductive load, a voltage is required at least equal to the back Emf generated in the load. That same voltage is impressed across the circuit interrupter which is carrying current as its resistance gradually increases from R=0 to R=.infin.. The product of this voltage and current represents the power dissipated in the circuit interrupter. The power dissipation occurs within the conducting path of the circuit interrupter, heating the confined low-speed or stationary gas between the contacts, and also at the boundaries of the conducting path, corroding the contacts. During the time required to transfer the current to the inductive load, if the circuit interrupter does not develop a high dielectric strength quickly enough, the dissipated power can destroy or otherwise deteriorate the elements of the circuit interrupter, in some cases preventing operation of the circuit interrupter altogether.